The present invention relates to a feed-back controller for controlling injection molding machines, and more particularly to a feed back controller for controlling a control target which operational conditions are different in accordance with operational purposes.
Generally, an injection unit 10, as illustrated in FIG. 1, comprises an injection cylinder 16 driven by a discharge hydraulic pressure supplied through a switching valve 14 from a hydraulic pump 12 and an injection screw 18 moved within a barrel 18a in forward and backward directions by the injection cylinder 16. Under the control of the feed-back controller, the injection unit 10 is moved in the forward and backward directions by a driving apparatus which is not illustrated so that when an injection nozzle 20 as a top portion thereof touches with a mold 22 closed so as to inject a molten resin into the mold 22 for forming a molded article.
The above injection unit 10 including the switching valve 14 is controlled by a control unit 24. In this case, for the control target, for example, the injection screw 18, the operational state or position thereof are changed in accordance with operational purposes or the molding operation and the purge operation. In the purge operation, the injection unit 10 is positioned as retreated.
The operational state is automatically changed in accordance with the operational purposes for remarkable improvements in operational facilitation and safety of the injection molding machine.
The above control unit may, however, has the following problems to be solved.
In the conventional control unit, the injection screw 18 as the control target is controlled only in the operational states or the advanced and retreated positions so as to adjust the molding operation and the purge operation, but never controlled in motions such as the injection speed. Namely, under the conventional control of the injection unit 10, the injection speed remains unchanged between in the molding operation and the purge operation, although in the molding operation, the injection speed should be set higher than that in the purge operation. If, in the molding operation, the injection speed is lower than the required speed, this results in a low responsibility of the injection unit thereby to deteriorate the quality of the molded article. If, in the purge operation, the injection speed is higher than the required speed, this results in generation of a hunching phenomenon thereby raising the problem in safety.
In the above circumstances, it had been required to develop an apparatus for controlling positions, injection speed and injection pressure of the injection screw in the injection molding machine so as to adjust different operational conditions such as the molding operation and the purge operation.